1. Field of the Invention
The present invention relates to a syringe, and more particularly to a safety syringe that can safely hold a used needle and prevent the syringe from being used more than once.
2. Description of Related Art
To keep doctors, nurses or workers who deal with discarded syringes from being injured or infected by used needles, safety syringes with retractable needles have been designed such as the syringe in Taiwan Patent No. 356013. A conventional safety syringe has a hollow barrel, a plunger and a needle hub with a needle. The needle hub of the conventional safety syringe has an axial locking chamber, and the plunger has a proximal end and a protruding head. The protruding head is formed on the proximal end of the plunger. After injecting a medicine into a body, the proximal end of the plunger is pushed toward the needle hub, and the protruding end of the plunger is mounted inside the axial locking chamber in the needle hub. When a user pulls the plunger back, the needle hub will move inside the hollow barrel to protect a user from being hurt.
Because the needle hub is made of plastic and the protruding head of the plunger is made of a resilient material, the protruding head can be pressed into the axial locking chamber in the needle hub. However, when pulling the plunger with the needle hub back inside the hollow barrel, the needle hub easily separates from the plunger. To overcome the disadvantage, the axial locking chamber is made smaller to securely hold the protruding head of the plunger, but then the protruding head is hard to press into the axial locking chamber in the needle hub.
To overcome the shortcomings of conventional safety syringes, the present invention provides a safety syringe to mitigate or obviate the aforementioned problem.